Obesity and hyperglycemia in pregnancy impact fetal growth through over-nutrition and may stress the feta pancreas. Such intrauterine programming events affect birth weight and raise the offspring's risk trajectory for future obesity, type 2 diabetes, cardiovascular disease and premature death. This vicious cycle, through which female offspring of mothers with diabetes are themselves more likely to develop diabetes prior to delivery, transmits the burden of morbidity from one generation to the next. This tragic but preventable trend likely underlies the alarming increase in gestational and type 2 diabetes. We propose to conduct a randomized controlled trial in 400 overweight or obese pregnant Puerto Rican women (free of diabetes) and their infants, to favorably impact metabolic health in mothers and infants. Women presenting before 20 gestational weeks will be block randomized to a lifestyle modification intervention or standard care control group. Puerto Rico is a predominantly Hispanic U.S. territory with among the lowest levels of physical activity and fruit, vegetable and whole grain intake, and the highest rates of diabetes, childhood obesity and infant mortality of all U.S. jurisdictions; nevertheless, recruitment rates for research studies ae higher here than elsewhere in the U.S.. The intervention will be conducted in pregnant women and their infants, focusing on improving: (1) physical activity levels, (2) diet quality and calori intake, (3) behavioral imprinting and (4) prenatal care. The intervention will be delivered through six intensive core group sessions (10 participants per group), followed by booster sessions and phone calls, and will continue during lactation through the first postpartum year. We will evaluate whether the combined intervention will: (1) increase the percent of women with adequate gestational weight gain, (2) optimize early infant growth and (3) achieve adequate retention and compliance. As secondary aims, we will evaluate whether the interventions improve insulin sensitivity and beta-cell function in the women and fasting insulin concentrations in their infants. This study will also help us to work through the logistical and other barriers to develop more effective ways to intervene during pregnancy to maximally reduce cardio-metabolic risk trajectories of future generations. Undertaking this study in Puerto Rico will address a major health disparity common to many parts of the US, whilst also advancing knowledge about how early life risk factors could be influenced to reduce metabolic risk in young women and their offspring.